This invention relates to apparatus for measuring the flow of a fluid mass.
In this specification the term xe2x80x9cfluidxe2x80x9d is intended to refer to any flowing substance whether it may be liquid or a gaseous or a polyphase substance such as a liquid/solid or a liquid/gas.
Various methods are known for the measurement of the flow of a fluid mass and in particular it is known to use flow meters based on the Coriolis effect because they are capable of measuring the mass flow directly and are relatively insensitive to the properties, such as density and viscosity, of the fluid being measured. However, one of the main disadvantages of flow meters based on the Coriolis effect measurement is because the Coriolis forces generated are generally very small, the measurements are subject to interference from effects which are difficult to suppress.
Boom R J in xe2x80x9cA User""s Perspective for Coriolis Flow Metersxe2x80x9d 44th Annual Symposium on Instrumentation for the Processes Industry 1989 referred on pages 7-10 to some patents granted in the 1950""s for xe2x80x9cgyroscopic mass flow metersxe2x80x9d. All of these early meters involved curved members, a means of oscillation/vibration, and some sort of flexible coupling or slip joints and all attempted to measure the torque caused by the gyroscopic (Coriolis) effect. Such early gyroscopic meters were failures and all exhibited a common problem that because the Coriolis forces were small compared to other forces, then it was not possible to obtain accurate readings.
U.S. Pat. No. 3,927,565 describes an apparatus for measuring the mass flow of fluid and utilises a rectilinear pipe which can be rotated about an axis which is not parallel with the longitudinal axis of the pipe. The apparatus also includes a means for making the fluid flow through the pipe and means for measuring the force which the fluid flowing through the pipe exerts on a segment of the pipe.
U.S. Pat. No. 4,109,524 describes another method of measuring the mass flow rate using the Coriolis effect and describes an apparatus which includes a conduit having sections. A section of one end of the conduit is reciprocated and the torque generated by the Coriolis force is measured.
U.S. Pat. No. 4,252,028 describes an apparatus for measuring mass flow and utilises a plurality of channels which are provided in one or more conduits which rotate or oscillate as a common unit. Additive streams flow to the channels in one direction and subtractive streams are flowed through the channels in the opposite direction and the Coriolis force thereby imposed on the conduit is measured.
The invention provides an improved or at least alternative form of Coriolis flow meter.
In broad terms in one aspect the invention comprises a flow meter based on the Coriolis effect comprising a substantially U shaped tube driven in a controlled oscillatory motion about an axis to generate in the fluid within the tube a measurable bidirectional force, said U tube including flexible couplings intermediate of the length of the tube and adapted to allow the tube to be oscillated at a frequency which is not necessarily the resonant frequency of the tube.
In broad terms in another aspect the comprises a fluid flow meter based on the Coriolis effect comprising two U shaped tubes each including flexible couplings intermediate of their length and each being adapted to be excited by an oscillatory motion in which the motion in one tube is 180xc2x0 out of phase with the other tube and wherein the fluid flow through the tubes is in the same direction, means being provided to measure the difference in oscillatory force between the two tubes.
In broad terms in a further aspect the invention comprises a fluid flow meter based on the Coriolis effect comprising two U shaped tubes each including flexible couplings intermediate of their length and each being adapted to be excited by an oscillatory motion in which the motion in one tube is in phase with the other tube and wherein the fluid flow through the tubes is in the opposite direction, means being provided to measure the difference in oscillatory force between the two tubes.